FAIR VALUE MEASUREMENT - Valuation Techniques and Inputs for Level 3 Fair Value Measurements (Details) - Level 3 - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Interest-bearing deposits | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total Liabilities	$ 300,000,000	$ 293,000,000
Interest-bearing deposits | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Mean reversion (as a percent)	1.00%	1.00%
Forward price (as a percent)	99.08%	98.79%
Interest-bearing deposits | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Mean reversion (as a percent)	20.00%	20.00%
Forward price (as a percent)	99.65%	104.07%
Interest-bearing deposits | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Mean reversion (as a percent)	10.50%	10.50%
Forward price (as a percent)	99.13%	100.19%
Federal funds purchased and securities loaned or sold under agreement to repurchase | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total Liabilities	$ 765,000,000	$ 849,000,000
Federal funds purchased and securities loaned or sold under agreement to repurchase | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Interest rate (as a percent)	1.11%	0.62%
Federal funds purchased and securities loaned or sold under agreement to repurchase | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Interest rate (as a percent)	2.17%	2.19%
Federal funds purchased and securities loaned or sold under agreement to repurchase | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Interest rate (as a percent)	2.00%	1.99%
Short-term borrowings and long-term debt | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total Liabilities	$ 11,377,000,000	$ 9,774,000,000
Short-term borrowings and long-term debt | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Mean reversion (as a percent)		1.00%
Forward price (as a percent)	69.30%	69.05%
Commodity volatility (as a percent)		2.00%
Commodity correlation (as a percent)		(41.61%)
Short-term borrowings and long-term debt | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Mean reversion (as a percent)		20.00%
Forward price (as a percent)	193.63%	235.35%
Commodity volatility (as a percent)		32.19%
Commodity correlation (as a percent)		90.42%
Short-term borrowings and long-term debt | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Mean reversion (as a percent)		10.50%
Forward price (as a percent)	105.10%	103.28%
Commodity volatility (as a percent)		17.07%
Commodity correlation (as a percent)		52.85%
Trading account assets and liabilities | Interest rate contracts | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)	$ 3,679,000,000	$ 4,897,000,000
Trading account assets and liabilities | Interest rate contracts | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	10.36%
Mean reversion (as a percent)	1.00%	1.00%
IR log-normal volatility		1.00%
Trading account assets and liabilities | Interest rate contracts | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	79.60%
Mean reversion (as a percent)	20.00%	20.00%
IR log-normal volatility		93.97%
Trading account assets and liabilities | Interest rate contracts | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	59.26%
Mean reversion (as a percent)	10.50%	10.50%
IR log-normal volatility		62.72%
Trading account assets and liabilities | Foreign exchange contracts | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)	$ 906,000,000	$ 1,110,000,000
Trading account assets and liabilities | Foreign exchange contracts | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)	0.00%
FX Volatility (as a percent)	5.98%	1.39%
IR Basis (as a percent)	(0.99%)
IR-IR correlation (as a percent)	(51.00%)
IR-FX Correlation (as a percent)	(10.09%)
Trading account assets and liabilities | Foreign exchange contracts | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)	6.02%
FX Volatility (as a percent)	20.23%	26.85%
IR Basis (as a percent)	0.38%
IR-IR correlation (as a percent)	40.00%
IR-FX Correlation (as a percent)	60.00%
Trading account assets and liabilities | Foreign exchange contracts | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)	1.68%
FX Volatility (as a percent)	10.45%	15.18%
IR Basis (as a percent)	(0.04%)
IR-IR correlation (as a percent)	35.65%
IR-FX Correlation (as a percent)	49.13%
Trading account assets and liabilities | Foreign exchange contracts | Cash flow
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)		$ 134,000,000
Trading account assets and liabilities | Foreign exchange contracts | Cash flow | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)		0.04%
IR Basis (as a percent)		(0.85%)
IR-IR correlation (as a percent)		40.00%
IR-FX Correlation (as a percent)		16.41%
Trading account assets and liabilities | Foreign exchange contracts | Cash flow | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)		6.57%
IR Basis (as a percent)		(0.49%)
IR-IR correlation (as a percent)		50.00%
IR-FX Correlation (as a percent)		60.00%
Trading account assets and liabilities | Foreign exchange contracts | Cash flow | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)		2.66%
IR Basis (as a percent)		(0.84%)
IR-IR correlation (as a percent)		41.27%
IR-FX Correlation (as a percent)		49.52%
Trading account assets and liabilities | Equity contracts | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)	$ 2,977,000,000	$ 2,701,000,000
Trading account assets and liabilities | Equity contracts | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Equity volatility (as a percent)	3.00%	3.00%
Forward price (as a percent)	69.30%	69.05%
Equity-FX correlation		(60.70%)
Equity-IR correlation (as a percent)		(35.00%)
Yield volatility		3.55%
Equity-equity correlation		(87.70%)
Trading account assets and liabilities | Equity contracts | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Equity volatility (as a percent)	54.00%	97.78%
Forward price (as a percent)	114.48%	144.61%
Equity-FX correlation		28.20%
Equity-IR correlation (as a percent)		41.00%
Yield volatility		14.77%
Equity-equity correlation		96.50%
Trading account assets and liabilities | Equity contracts | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Equity volatility (as a percent)	24.61%	29.52%
Forward price (as a percent)	94.45%	94.28%
Equity-FX correlation		(26.28%)
Equity-IR correlation (as a percent)		(15.65%)
Yield volatility		9.29%
Equity-equity correlation		67.45%
Trading account assets and liabilities | Commodity contracts | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)	$ 2,939,000,000	$ 2,955,000,000
Trading account assets and liabilities | Commodity contracts | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Forward price (as a percent)	41.12%	35.74%
Commodity volatility (as a percent)	8.99%	2.00%
Commodity correlation (as a percent)	(38.81%)	(41.61%)
Trading account assets and liabilities | Commodity contracts | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Forward price (as a percent)	405.15%	235.35%
Commodity volatility (as a percent)	49.49%	32.19%
Commodity correlation (as a percent)	90.59%	90.42%
Trading account assets and liabilities | Commodity contracts | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Forward price (as a percent)	141.97%	119.99%
Commodity volatility (as a percent)	27.04%	17.07%
Commodity correlation (as a percent)	37.73%	52.85%
Trading account assets and liabilities | Credit derivatives | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)	$ 2,187,000,000	$ 2,786,000,000
Trading account assets and liabilities | Credit derivatives | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Recovery rate (as a percent)	12.22%	20.00%
Trading account assets and liabilities | Credit derivatives | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Recovery rate (as a percent)	55.00%	75.00%
Trading account assets and liabilities | Credit derivatives | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Recovery rate (as a percent)	36.93%	39.75%
Trading account assets and liabilities | Credit derivatives | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)	$ 949,000,000	$ 1,403,000,000
Trading account assets and liabilities | Credit derivatives | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		$ 1.00
Credit spread (as a percent)	0.02%	0.03%
Credit correlation (as a percent)	10.00%	5.00%
Upfront points (as a percent)	10.94%	6.00%
Trading account assets and liabilities | Credit derivatives | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		$ 167.00
Credit spread (as a percent)	14.07%	15.15%
Credit correlation (as a percent)	85.00%	90.00%
Upfront points (as a percent)	99.00%	99.90%
Trading account assets and liabilities | Credit derivatives | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		$ 77.35
Credit spread (as a percent)	1.12%	2.56%
Credit correlation (as a percent)	42.46%	34.27%
Upfront points (as a percent)	68.80%	72.89%
Nontrading derivatives and other financial assets and liabilities | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Derivatives (gross)	$ 16,000,000	$ 42,000,000
Nontrading derivatives and other financial assets and liabilities | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Recovery rate (as a percent)		40.00%
Upfront points (as a percent)		16.00%
Redemption rate (as a percent)	10.70%	3.92%
Nontrading derivatives and other financial assets and liabilities | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Recovery rate (as a percent)		40.00%
Upfront points (as a percent)		20.50%
Redemption rate (as a percent)	99.50%	99.58%
Nontrading derivatives and other financial assets and liabilities | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Recovery rate (as a percent)		40.00%
Upfront points (as a percent)		18.78%
Redemption rate (as a percent)	74.48%	74.69%
Securities sold, not yet purchased | Trading account liabilities | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total Liabilities	$ 612,000,000	$ 1,056,000,000
Securities sold, not yet purchased | Trading account liabilities | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	26.85%	12.86%
Securities sold, not yet purchased | Trading account liabilities | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	77.79%	75.50%
Securities sold, not yet purchased | Trading account liabilities | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	64.45%	61.73%
Mortgage-backed securities | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 480,000,000	$ 509,000,000
Mortgage-backed securities | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	5.90	5.50
Mortgage-backed securities | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	102.90	113.48
Mortgage-backed securities | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	73.64	61.74
Mortgage-backed securities | Yield analysis
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 339,000,000	$ 368,000,000
Mortgage-backed securities | Yield analysis | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	1.55%	1.90%
Mortgage-backed securities | Yield analysis | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	13.72%	14.54%
Mortgage-backed securities | Yield analysis | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	4.96%	4.34%
State and municipal, foreign government, corporate, and other debt securities | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 1,535,000,000
State and municipal, foreign government, corporate, and other debt securities | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 2,830,000,000	$ 3,308,000,000
State and municipal, foreign government, corporate, and other debt securities | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		15.00
State and municipal, foreign government, corporate, and other debt securities | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		103.60
State and municipal, foreign government, corporate, and other debt securities | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		89.93
State and municipal, foreign government, corporate, and other debt securities | Cash flow
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets		$ 1,513,000,000
State and municipal, foreign government, corporate, and other debt securities | Cash flow | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)		0.35%
State and municipal, foreign government, corporate, and other debt securities | Cash flow | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)		6.00%
State and municipal, foreign government, corporate, and other debt securities | Cash flow | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Credit spread (as a percent)		2.30%
Non-mortgage debt securities | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	2.17%
Credit spread (as a percent)	0.35%
Non-mortgage debt securities | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	16.04%
Credit spread (as a percent)	3.75%
Non-mortgage debt securities | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	5.92%
Credit spread (as a percent)	2.33%
Non-mortgage debt securities | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	$ 21.03
Non-mortgage debt securities | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	108.46
Non-mortgage debt securities | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	88.99
Equity securities | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	80,000,000	$ 69,000,000
Equity securities | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		0.48
Equity securities | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		104.00
Equity securities | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		22.19
Equity securities | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	156,000,000	58,000,000
Equity securities | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	0.09
Equity securities | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	1,402.80
Equity securities | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	640.33
Asset-backed securities | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	2,387,000,000	2,454,000,000
Asset-backed securities | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	36.50	4.00
Asset-backed securities | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	100.00	100.00
Asset-backed securities | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset	85.34	71.51
Non-marketable equity securities | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 283,000,000	$ 726,000,000
Non-marketable equity securities | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Discount to price (as a percent)	0.00%	0.00%
Price-to-book ratio	0.05
Non-marketable equity securities | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Discount to price (as a percent)	100.00%	90.00%
Price-to-book ratio	1.12
Non-marketable equity securities | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Discount to price (as a percent)	9.71%	13.36%
Price-to-book ratio	0.85
Non-marketable equity securities | Comparables Analysis
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 502,000,000	$ 565,000,000
Non-marketable equity securities | Comparables Analysis | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		$ 0.00
EBITDA multiples	7.3	6.8
Price-to-book ratio		0.32
Non-marketable equity securities | Comparables Analysis | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		$ 113.23
EBITDA multiples	13.3	10.1
Price-to-book ratio		1.03
Non-marketable equity securities | Comparables Analysis | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		$ 54.40
EBITDA multiples	8.94	8.62
Price-to-book ratio		0.87
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 664,000,000	$ 1,496,000,000
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	26.85%
Interest rate (as a percent)		(0.51%)
IR log-normal volatility		12.86%
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	77.79%
Interest rate (as a percent)		5.76%
IR log-normal volatility		75.50%
Federal funds sold and securities borrowed or purchased under agreements to resell | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
IR normal volatility (as a percent)	64.45%
Interest rate (as a percent)		2.80%
IR log-normal volatility		61.73%
Loans and leases | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 388,000,000
Loans and leases | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, liability	29.16
Loans and leases | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, liability	146.83
Loans and leases | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, liability	137.53
Loans and leases | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 150,000,000
Loans and leases | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	2.53%
Loans and leases | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	3.09%
Loans and leases | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	3.02%
Mortgage servicing rights | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 88,000,000
Mortgage servicing rights | Model-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
WAL (in years)	4 years 22 days
Mortgage servicing rights | Model-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
WAL (in years)	7 years 3 months 18 days
Mortgage servicing rights | Model-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
WAL (in years)	6 years 7 days
Mortgage servicing rights | Cash flow
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets	$ 465,000,000	$ 1,473,000,000
Mortgage servicing rights | Cash flow | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	8.00%	4.20%
WAL (in years)		3 years 6 months 11 days
Mortgage servicing rights | Cash flow | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	18.96%	20.56%
WAL (in years)		7 years 2 months 27 days
Mortgage servicing rights | Cash flow | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)	12.59%	9.32%
WAL (in years)		5 years 9 months 29 days
Loans | Model-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets		$ 79,000,000
Loans | Price-based
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets		258,000,000
Loans | Price-based | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		31.55
Loans | Price-based | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		105.74
Loans | Price-based | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Price, asset		56.46
Loans | Yield analysis
Fair Value Inputs Assets Liabilities Quantitative Information
Total assets		$ 221,000,000
Loans | Yield analysis | Minimum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)		2.75%
Loans | Yield analysis | Maximum
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)		20.00%
Loans | Yield analysis | Weighted Average
Fair Value Inputs Assets Liabilities Quantitative Information
Yield (as a percent)		11.09%